Many times, an unfortunate consequence of modern back surgery, whether lumbar, thoracic, or cervical surgery, is the formation of post-operative scar tissue. Scar formation surrounding the dura and nerve roots oftentimes will compress the nerve roots and cauda equina, thereby producing neural complications such as persistent low back pain, sciatica, and/or bowel and bladder dysfunction. Multiple revision operations may prove necessary due to recurrent disk herniation, post-operative spinal stenosis (iatrogenic or acquired), or because of exuberant epidural fibrosis.
Scar tissue formation after laminectomies and laminotomies for disk excision or a decompressive laminectomy for spinal stenosis present both surgeon and patient with an additional post-operative concern. Laminectomies and laminotomies frequently remove bone tissue and leave the dura exposed. Post laminectomy scar tissue, also termed epidural fibrosis, is primarily formed from fibrous connective tissue and develops in the post-operative hematoma that forms between the paraspinous muscles and the dura. The dura is relatively thin and can easily be injured during surgery. In particular, the dura is susceptible to damage during revision surgery when scar tissue adheres to the dura making it difficult for the surgeon to perform an adequate neurolysis. Thus, a method is needed for protecting the dura from scar tissue adhesion.
At the present time methods to minimize the amount of scar tissue include the use of autogenous fat grafts, gelatin foams or sponges, or microfibullary collagen as an interposing protective layer between the spinal dura and the adjacent viscera. Other biological substances and chemical compounds that have been tested experimentally for their usefulness in animals include bone grafts, microfibrillar collagen, elastase, polyethylene, mylar, dacron, teflon and methylmethacrylate.
Autogenous fat grafts have been used following laminectomies as early as 1964. The fat is placed over the exposed dura after removal of the lamina or a portion of the lamina. The fat provides a protective barrier for the dura, and may limit scar formation between the muscle and the dural tissue. However, fat grafts are known to frequently adhere to the dura. These adhesions complicate revision surgery because they require tedious dissection by the orthopaedic or neurosurgeon. Fat grafts are preferably harvested from a sight close to the surgical incision, such as the subdermal areolar tissue bed. However, unless the patients are overweight, fat harvesting from nearby locations is not always possible, particularly in multiple laminectomy procedures. Further, fat harvesting may require a second incision. The incisions at the secondary locations may sometimes lead to complications such as hematoma formation or dimpling in the skin.
Other substances are used where fat grafts are not possible or desired. Gelatin foam (such as Gelfoam.RTM. sponge, supplied by Upjohn Company Inc., Kalamazoo, Mich.), or polylactic acid (PLA) is a useful substitute for autogenous fat grafts. This material is also placed over the dura to reduce scar formation. There is some controversy concerning the preference of gelatin foams or sponges versus fat; however, neither is optimal. Like fat, gelatin foams or sponges may move out of position following surgery. Furthermore, while fat and gelatin foams may form a barrier between the visceral tissue and the dura, there is a propensity for both fat and gelatin foam or sponge to adhere to the dura. Neither fat nor gelatin foam provides adequate physical protection to the cauda equina.
A mechanical barrier that would provide support to the spinal dura as well as reduce scar formation is needed. U.S. Pat. No. 4,013,078 to Feild discloses a device for preventing adhesions between the patient's dura and spinal nerves and other anatomic structures following spinal surgery. The device includes a conduit sheath of teflon or silicone that is positioned in close proximity to the nerve root. Like the previous protective overlay substances, such a device is invasive to the neuroforamen and anchors directly to the dura. This in turn would promote adhesions between the dura and the protecting device creating unnecessary complications for revision surgery.
In order to minimize the surgical time for dissection, minimize nerve injury and minimize dural tears a spinal cord protection device should be simple to insert, non-invasive to the dura and maintain a distance from the neural tissues. Preferably, anchoring means should contact bone instead of tissue prone to scar formation to minimize post-operative epidural fibrosis. Finally, the optimal mechanical device is readily contoured to provide a customized mechanical barrier to prevent dural or nerve root injury. Preferably, the device is adaptable in design to accommodate other surgical devices used in back surgery. Such a device is provided in the detailed description of this invention.